<!DOCTYPE html>
<html lang="en">

<head>
  <meta charset="UTF-8">
  <meta http-equiv="X-UA-Compatible" content="IE=edge">
  <meta name="viewport" content="width=device-width, initial-scale=1.0">
  <style>
    #result {
      width: 200px;
      height: 100px;
      border: 1px solid
    }
  </style>
  <title>Document</title>
</head>

<body>
  <button>点击发送请求</button>
  <button>点击取消请求</button>
  <div id="result"></div>

</body>

<script>
  const btns = document.querySelectorAll('button')
  const result = document.getElementById('result')
  //得要先把这个变量放在最外面,并且必须要用let
  let xhr = null
  btns[0].addEventListener('click', function () {
    xhr = new XMLHttpRequest()
    xhr.open('GET', 'http://127.0.0.1:8000/delay')
    xhr.send();
    xhr.onreadystatechange = function () {
      if (xhr.readyState === 4) {
        if (xhr.status >= 200 && xhr.status < 300) {
          console.log(xhr.response);
          result.innerHTML = xhr.response
        }
      }
    }
  })

  //abort 可以取消请求
  btns[1].onclick = function () {
    xhr.abort()
  }
</script>

</html>